Python 3.0 was released in December 2008 and was admitted to be somewhat experimental. At that point, PostgreSQL 8.4 was already in some kind of freeze, so adding a feature as signicant as Python 3 support was not feasible at that point.

In fact, we opted to do two significant rounds of fixing/enhancing/refactoring of PL/Python before tackling Python 3 support: fixed byte string (bytea) support and Unicode support. Both of those benefit Python 2 users, and they made the eventual port to Python 3 quite simple.

PostgreSQL 8.5 might release around May 2010. Debian squeeze is currently in testing and doesn't even contain Python 2.6 or Python 3.1 yet, due to some technical problems and a bit of infighting. Debian freezes in March 2010, which means without PostgreSQL 8.5 but hopefully with Python 2.6 and 3.1. The final release of squeeze should then be later in 2010, which means the earliest that a significant number of Debian users are going to look into moving any of their code at all nearer to Python 3 (via 2.6) is going to be late 2010. (Other operating system distributions will have other schedules, of course.)

The next Debian release (squeeze+1), which will presumably include PostgreSQL 8.5 or later and a solid Python 3.x environment, will then not be released before January 2012, if we believe the current 18-months-plus-slip cycle of Debian. So it will be mid-2012 until significant numbers have upgraded Debian and PostgreSQL to the then-current versions. If you are sticking to a stable and supported operating system environment, this is the earliest time you actually have the option to migrate to the Python 3 variant of PL/Python across the board for your applications. Of course in practice this is not going to be the first thing you are going to do, so by the time you actually port everything, it might be late 2012 or even 2013. Also, if you are heavily invested in PL/Python, you are probably not going to upgrade much your other Python code before PL/Python is ready.

This will then be 3 years after the PL/Python 3 code is written and 4 years after the release of Python 3.0. And 2 years before Python 2.x is expected to go out of maintenance in 2015.